1. Field of the Invention
The present invention relates to a fuel supply system of an internal combustion engine improving a control method of a high-pressure pump.
2. Description of Related Art
A direct injection type engine, which injects fuel directly into cylinders, needs to promote atomization of the injected fuel by increasing an injection pressure in order to ensure combustibility. Therefore, in the direct injection type engine, a low-pressure pump draws the fuel from a fuel tank, and a high-pressure pump pressurizes the fuel to a high pressure and pressure-feeds the fuel to fuel injection valves. For instance, a high-pressure pump disclosed in JP-A-2001-304071 (pages 3, 4, etc.) drives a plunger, which reciprocates in a pump chamber for suctioning and discharging the fuel, with a camshaft of the engine. The high-pressure pump regulates a fuel discharge quantity (or a fuel pressure for supplying the fuel to the fuel injection valves) by opening and closing a suction passage of the pump chamber with an electromagnetic valve.
Generally, a phase of a cam (or a phase of the plunger) is recognized based on a crank angle sensed by a crank angle sensor during operation of the engine, and energization of the electromagnetic valve is controlled based on the crank angle. Thus, opening timing and closing timing of the electromagnetic valve with respect to the reciprocating movement of the plunger, which is driven by the camshaft of the engine, is controlled, and the fuel discharge quantity is controlled. Thus, the high-pressure pump is controlled. Therefore, the crank angle (the phase of the cam) cannot be sensed before crank angle determination, or cylinder determination, based on the output signal of the crank angle sensor and the like is completed during an engine starting period. Accordingly, the opening timing and the closing timing of the electromagnetic valve with respect to the reciprocating movement of the plunger cannot be controlled. Therefore, the suction passage of the high-pressure pump is held at the opened state by holding the electromagnetic valve at the opened state so that the fuel supplied by the low-pressure pump can be supplied to the fuel injection valve side before the completion of the crank angle determination during the engine starting period.
In the high-pressure pump, the electromagnetic valve opens and closes at each reciprocating movement of the plunger during the operation of the engine. Therefore, operation noise (collision noise) is generated by collision between a valve member and a valve seat or collision between a movable portion and a stopper portion accompanying the opening and closing of the electromagnetic valve. The operation noise is not audible to vehicle occupants because of engine sound or travel noises such as a road noise caused during the travel when the engine is in an operation state in which an engine rotation speed is high. The engine sound and the other noises decrease when the engine is in another operation state in which the engine rotation speed is low (for instance, an idling operation state). In such a case, there is a possibility that the operation sound of the electromagnetic valve is audible to the vehicle occupants, so the vehicle occupants suffer discomfort.
In the control of the high-pressure pump of the related art explained above, the electromagnetic valve is held at the opened state and the suction passage of the high-pressure pump is held at the opened state until the crank angle determination is completed during the engine starting period. Accordingly, the fuel supplied by the low-pressure pump is scarcely pressurized by the high-pressure pump and is supplied toward the fuel injection valves while the fuel remains low-pressure. Therefore, the injected fuel cannot be atomized sufficiently in an early stage of the engine starting period. As a result, the combustibility is deteriorated, and starting performance and exhaust emission are deteriorated.